Contrasting parasite communities among allopatric colour morphs of the Lake Tanganyika cichlid Tropheus

Abstract

BackgroundAdaptation to different ecological environments is thought to drive ecological speciation. This phenomenon culminates in the radiations of cichlid fishes in the African Great Lakes. Multiple characteristic traits of cichlids, targeted by natural or sexual selection, are considered among the driving factors of these radiations. Parasites and pathogens have been suggested to initiate or accelerate speciation by triggering both natural and sexual selection. Three prerequisites for parasite-driven speciation can be inferred from ecological speciation theory. The first prerequisite is that different populations experience divergent infection levels. The second prerequisite is that these infection levels cause divergent selection and facilitate adaptive divergence. The third prerequisite is that parasite-driven adaptive divergence facilitates the evolution of reproductive isolation. Here we investigate the first and the second prerequisite in allopatric chromatically differentiated lineages of the rock-dwelling cichlid Tropheus spp. from southern Lake Tanganyika (Central Africa). Macroparasite communities were screened in eight populations belonging to five different colour morphs.ResultsParasite communities were mainly composed of acanthocephalans, nematodes, monogeneans, copepods, branchiurans, and digeneans. In two consecutive years (2011 and 2012), we observed significant variation across populations for infection with acanthocephalans, nematodes, monogeneans of the genera Gyrodactylus and Cichlidogyrus, and the copepod Ergasilus spp. Overall, parasite community composition differed significantly between populations of different colour morphs. Differences in parasite community composition were stable in time. The genetic structure of Tropheus populations was strong and showed a significant isolation-by-distance pattern, confirming that spatial isolation is limiting host dispersal. Correlations between parasite community composition and Tropheus genetic differentiation were not significant, suggesting that host dispersal does not influence parasite community diversification.ConclusionsSubject to alternating episodes of isolation and secondary contact because of lake level fluctuations, Tropheus colour morphs are believed to accumulate and maintain genetic differentiation through a combination of vicariance, philopatric behaviour and mate discrimination. Provided that the observed contrasts in parasitism facilitate adaptive divergence among populations in allopatry (which is the current situation), and promote the evolution of reproductive isolation during episodes of sympatry, parasites might facilitate speciation in this genus.

Intermediate number of major histocompatibility complex class IIB length variants relates to enlarged perivisceral fat deposits in the blunt‐head cichlid Tropheus moorii

“…I PI was correlated with body size, as larger individuals were infected by a higher number of parasites (Table ). Consistent with earlier results (Raeymaekers et al ., ), infection patterns differed between the host populations, but not between sexes. There was no significant effect of number of MHC length variants or perivisceral fat deposits on I PI (Table S1; linear term: F 1,221 = 0.41, P = 0.5225, quadratic term: F 1,221 = 0.31, P = 0.5788; Fig.…”

“…Many studies have focused on its ecology and population history (Takamura, ; Yanagisawa & Nishida, ; Baric et al ., ; Sturmbauer et al ., ; Salzburger et al ., ; Egger et al ., ; Koblmüller et al ., ). Recently, we investigated the spatial structure of parasite communities in T. moorii (Raeymaekers et al ., ). We found that allopatric T. moorii colour morphs were infected by contrasting parasite communities and that this pattern is stable, at least over a period of 2 years.…”

Divergent parasite infections in sympatric cichlid species in Lake Victoria

“…Over the recent years, studies have begun to explore differentiation in parasitism among morphs and incipient species of freshwater fish, mainly in species‐poor communities (Knudsen et al ., , ; MacColl, ; Eizaguirre et al ., ; Natsopoulou et al ., ; Karvonen et al ., ,b, ; Raeymaekers et al ., ; Anaya‐Rojas et al ., ; Siwertsson et al ., ) (but see Blais et al . (), Raeymaekers et al .…”

“…The first prerequisite of parasite‐mediated divergent selection in natural populations is that infections differ between diverging host populations. Currently, there is a growing body of literature describing differentiated parasite infections in ecotypes or closely related species particularly in freshwater fishes (Knudsen et al ., , ; MacColl, ; Eizaguirre et al ., ; Natsopoulou et al ., ; Karvonen et al ., ,b, ) including cichlid fishes (Blais et al ., ; Maan et al ., ; Raeymaekers et al ., ; Hablutzel et al ., , ). Overall, these studies suggest that conditions for parasite‐mediated divergent selection between ecological niches are not uncommon.…”

Immigrant and extrinsic hybrid inviability contribute to reproductive isolation between lake and river cichlid ecotypes

“…), as well as between different locations within a lake (Raeymaekers et al. ). Moreover, the water parameters also differ between different locations in the lake, and in particular lake water close to the estuary of the Lufubu River has very different chemical properties–closer to the riverine than to the lacustrine environment.…”